You are looking at 1 - 10 of 15 items for
- Author or Editor: A.C. Purvis x
Mitochondria isolated from the pericarp tissue of green bell pepper (Capsicum annuum L.) fruit and purified on a Percoll gradient produced superoxide in buffers aerated with oxygen. ADP and uncouplers of the electron transport chain reduced superoxide production. Disulfiram, an inhibitor of the alternative oxidase, enhanced superoxide production. Inhibitors of the ubiquinone-cytochrome bc1 complex had little effect on superoxide production by mitochondria which were insensitive to cyanide. Less superoxide was produced when DTT was used to reduce the sulfhydryl groups of the alternative oxidase protein and the enzyme was activated with pyruvate than when the sulfhydryl groups were oxidized with diamide. A role for the alternative oxidase in limiting the level of reactive oxygen species produced in stressed and senescing plant tissues is suggested.
It has long been observed that chilling injury of warm-season fruit and vegetables during postharvest storage as well as during early seedling growth can be mitigated by maintaining high relative humidities during the exposure to low temperatures. A strong correlation between transpiration rates and chilling injury was observed among the fruit of several PI lines of greenhouse-type and field-type Cucumis sativus L. differing in their susceptibility to chilling injury. Transpiration rates and chilling injury of the F1s from crosses between resistant and susceptible lines were intermediate. Immature fruit lost moisture at faster rates and chill injured more severely than mature fruit of the same genotype. Coatings, applied as postharvest treatments to the fruit either reduced or increased chilling injury depending on the concentration applied and whether or not they retarded or enhanced moisture loss during low temperature storage. Fruit coated with surfactant-based waxes lost more moisture and developed more chilling injury than uncoated fruit or fruit coated with carnauba wax or polyethylene emulsions. The causal relationship between transpiration at low temperatures and chilling injury is not known, primarily because the precise mechanism of chilling injury has not been unequivocally delineated. The manifestation of chilling injury, however, occurs concomitantly with an increase in respiratory rate. We have postulated that chilling injury is caused by active oxygen species generated when the mitochondrial electron transport chain is impaired. In studies with germinating seed, desiccation injury was associated with free radicals generated by mitochondria. Thus, desiccation at low temperatures may intensify respiratory activity resulting in the generation of oxygen free radicals and extensive peroxidative damage to cellular membranes and enzymes.
‘Marsh’ grapefruit (Citrus paradisi Macf.) harvested from the exterior canopy positions pitted more severely during storage at 5°C than did fruit harvested from the interior canopy of the same tree. The flavedo tissue of interior and exterior canopy fruit had similar calcium contents. Severity of pitting within a single lot of fruit also was not significantly correlated (r = - 0.24 ns) to the calcium content of the peel. Thus, the variation in susceptibility of grapefruit to chilling injury does not appear to be related to endogenous calcium content of the flavedo tissue.
‘Marsh‘ grapefruit (Citrus paradisi Macf.) harvested from the exterior canopy of the tree were more susceptible to chilling injury (CI) at 4.4°C than grapefruit harvested from the interior canopy of the same tree. No differences were found in the levels of total soluble carbohydrates, reducing sugars, and sucrose in the peels of the fruit from the 2 canopy depths. An unusual pattern of CI, remarkably similar to the pattern of citrus rust mite [Phyllocoptruta oleivora (Ashm.)] damage, was observed in several of the exterior canopy fruit. Although the fruit had no visible rust mite damage at harvest, fruit remaining on the tree developed the characteristic bronzing associated with rust mite injury within 2 to 3 weeks after the test fruit were harvested. It is suggested that environmental and biotic factors predispose grapefruit to CI.
Peel samples of ‘Marsh’ grapefruit (Citrus paradisi Macf.) from 2 separate chilling injury (CI) experiments conducted during the 1979–80 season were analyzed for proline. Proline levels were highest in the peel of grapefruit after the seasonal night temperatures reached their minimum and levels declined after night temperatures increased in the spring. The greatest resistance of grapefruit peel to CI during postharvest cold storage coincided with high proline concentrations. Peels of unexposed interior canopy fruit had higher proline contents and were also more resistant to CI than peels of exposed exterior canopy fruit. Proline accumulation may be a consequence of an environmental stress rather than a cause of hardening to the stress or a mechanism of resistance.
Chilling injury (CI) is an important postharvest physiological problem that limits the storage life of many warm-season fruits and vegetables. Variability exists among cultivars and CI appears to be related to moisture loss during low temperature storage. The relationship between moisture loss and CI was examined using fruit from 64 PI lines of field-grown Cucumis sativus. A wide variation existed among the lines in the sensitivity of their fruit to low temperatures. Fruit from 8 of the lines developed severe symptoms of CI after 5 days at 5°C and fruit from 21 lines developed no injury symptoms. CI symptoms developing during 2 and 4 days of storage at 15°C were highly significantly correlated with weight loss during the 5 days of storage at 5°C. Crosses were made between chilling-sensitive and chilling-resistant lines. CI symptoms of the F1 fruit were highly significantly correlated with weight loss during the 5 days of storage at 5°C.
One theory on the mechanism of chilling injury of tropical and subtropical fruits is that aerobic respiration is impaired at chilling temperatures and injury occurs from consequent accumulation of fermentation products. Therefore, O2 uptake and CO2 evolution by the flavedo (colored portion of peel) of chill-sensitive grapefruit (Citrus paradisi Macf.) and chill-resistant orange (Citrus sinensis (L.) Osbeck) tissue were measured by a manometric Warburg technique over a range of chilling and non-chilling temperatures to see if there were differences in respiratory activities of the 2 tissues. A break in the Arrhenius plot of CO2 evolution and O2 uptake by grapefruit tissues occurred at 12°C but no break was apparent in similar plots for orange tissue. Respiratory quotients for both orange and grapefruit were lower at chilling than non-chilling temperatures. When O2 uptake was determined in the presence of maximal inhibitory levels of cyanide and salicylhydroxamic acid, a large residual O2 uptake remained. At chilling temperatures, in the absence of cyanide, salicylhydroxamic acid reduced O2 uptake by grapefruit flavedo tissue by 30% but had no effect on O2 uptake by orange flavedo tissue in the absence of cyanide. The results indicate that extra-mitochondrial oxidases may have a role in chilling injury of grapefruit flavedo.
‘Marsh’ grapefruit (Citrus paradisi Macf.) were seal-packaged in low-density, polyethylene films ranging from 20 to 40 µm in thickness and stored at temperatures from 5 to 28°C for periods up to 109 days. Film thickness had a negligible effect on transpiration, respiratory gas exchange, and juice quality. Storage temperature had a negligible effect on transpiration of seal-packaged fruit. However, 28° storage temperature significantly affected acid concentration in both seal-packaged and unwaxed fruit, probably as a result of increased respiratory activity at high storage temperatures. Quality of both seal-packaged fruit and unwaxed fruit deteriorated in storage at 28°.
An emerging theory contends that chilling injury is due to oxidative damage resulting from the metabolic generation of active oxygen species. Mitochondria were isolated from chilling-sensitive (CS) and from conditioned chilling-resistant (CR) bell pepper fruit and their ability to generate superoxide determined by measuring the formation of adrenochrome from epinephrine. Mitochondria from CS fruit were sensitive to cyanide and produced superoxide when supplied with NADH, succinate, or malate-pyruvate. Mitochondria from CR fruit were insensitive to cyanide and sensitive to SHAM and produced little superoxide when supplied with respiratory substrates. ATP enhanced the production of superoxide and ADP reduced the production. Results suggest that the mitochondria are a major source of superoxide in CS plant tissue and the presence of the alternative pathway reduces the production of superoxide.
Four-year-old ‘Marsh’ grapefruit (Citrus paradisi Macf.) trees on trifoliate orange [Poncirus trifoliata (L.) Raf.] rootstock were temperature acclimated to 5°C in controlled environment facilities with approximately 400 μeinsteins m−2s−1 PAR. Total soluble carbohydrates and proline increased in both leaves and fruit flavedo as temperatures were progressively decreased. Maximum accumulation of carbohydrates occurred in leaves and flavedo at 10° ambient air. Both sucrose and reducing sugars increased in leaves at all acclimating temperatures, but only reducing sugars increased in the flavedo at temperatures below 15°. The concentration of proline was the greatest in the leaves and flavedo at 5°. Both total soluble carbohydrates and proline decreased during temperature deacclimation at 25°.